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• Factors driving rice straw and milk vetch mixture (MR) decomposition were studied. • Non-additive synergistic effects on biomass loss were observed in 55.6% of the sampled MR. • MR enhanced fungal abundance by 19.6–30.6% compared to a single residue. • Bacteria contributed more to residue decomposition than did fungi in paddy soils. • The increase in Peziza sp. and Reticulascus tulasneorum may drive MR decomposition. The co-incorporation of rice straw (RS) and milk vetch (MV) into paddy fields has been increasingly applied as a sustainable farming practice in southern China. Our previous study revealed the contribution of bacteria to the co-decomposition of the RS and MV mixture, although additional underlying factors driving the co-decomposition process need to be clarified. The present study further determined the succession of fungal communities and enzyme activity in the co-decomposition process of the RS and MV mixture. The results showed that non-additive synergistic effects on biomass loss were observed in 55.6% of the sampled RS and MV mixture during the co-decomposition process, stimulating mixture decomposition. Overall fungal abundance was 19.6–30.6% higher in the RS and MV mixture throughout the study than in the single residue. Fungal diversity and community structure were mainly affected by the sampling date rather than the type of residue. Specifically, mixing RS and MV significantly increased the abundance of Peziza sp. and Reticulascus tulasneorum (lignocellulose- and lignin-decomposing fungi) and exhibited higher activities of C- and N-related hydrolases than monospecific residues. Random forest (RF) models showed that bacteria contributed more to the residue decomposition and activities of C-related hydrolases, N-related hydrolases, and oxidases than fungi. However, both RF and partial least squares path models revealed that fungal abundance and community structure directly or indirectly affected the residue decomposition rate. These findings showed that mixing RS and MV could stimulate their decomposition by enhancing C-related hydrolase activity and Peziza sp. and Reticulascus tulasneorum abundance. [ABSTRACT FROM AUTHOR]

Although widely studied in grassland and forest ecosystems, dissolved organic nitrogen (DON), an important form of nitrogen (N) lost through leaching, has received little attention in cropland ecosystem research. A global literature review and partial least squares path modeling (PLS–PM) were adopted to assess the quantity and composition of N leaching loss under different cropping systems, soil types, and management practices, as well as to identify the major factors controlling DON leaching. Annual total dissolved nitrogen (TDN, organic + inorganic N) leaching under different cropping systems ranged from 4.0 to 383.2 kg N ha−1. Vegetable and rice production systems showed the greatest and least TDN leaching, respectively. Across different cropping systems, DON accounted for 4.7%–34.9% of TDN in leachate. The NH4+–N form of N leaching is negligible in most upland cropping systems (<2.3%), but not so in lowland rice systems. The largest ratio of DON leaching to TDN leaching was found in a rice–wheat rotation (34.9%). Catch crop slightly increased DON leaching; however, it greatly decreased TDN leaching. Cropping systems in which animal manure or plant compost was applied or lowland rice was included showed a relatively high DON leaching ratio. Accordingly, in investigating DON leaching, more attention should be focused on cropping systems with manure application or lowland rice systems. Compared with climatic conditions and soil properties, field management practices (irrigation, chemical N input, and manure amendments) proved to be the factors most strongly influencing DON leaching. This suggests that optimizing water and N management practices is the most effective way of reducing the risk of DON leaching and increasing N use efficiency, particularly for vegetable and rice production systems. [ABSTRACT FROM AUTHOR]

The practice of co‐incorporating rice straw and leguminous green manure (such as Chinese milk vetch) into paddy soils has become increasingly popular in the last 10 years, although its effect on soil CH4 emissions and microbial community structure is poorly understood. In this study, data from a 2‐year pot experiment were used to reveal the effects of the co‐incorporation of rice straw and Chinese milk vetch on CH4 emissions and methanogenic and methanotrophic communities in paddy soil. Five treatments were chosen: CK (unamended control), CF (inorganic fertilizer), FM (inorganic fertilizer and Chinese milk vetch, 20 g 10 kg−1 dry soil, 4.5 t ha−1), FR (inorganic fertilizer and rice straw, 20 g 10 kg−1 dry soil, 4.5 t ha−1) and FMR (inorganic fertilizer and Chinese milk vetch and rice straw mixture, 5 + 15 g 10 kg−1 dry soil, 1.125 + 2.375 t ha−1). Overall, the soil CH4 emissions in the 2 years under all residue treatments (104.4–122.8 and 83.3–133.3 g CH4 m−2) were higher than those in CK (57.0 and 20.7 g CH4 m−2) and CF (71.8 and 21.9 g CH4 m−2) treatments. The FMR treatment decreased CH4 emissions when compared with FM and FR, especially in the second year. A higher abundance of methanogens (mcrA gene copies) was found under the plant residue‐treated soils (4.35 × 108 g−1 dry soil on average) and FM increased the abundance of methanotrophs (pmoA gene copies, 2.68 × 106 g−1 dry soil). Application of plant residues changed the methanogenic and methanotrophic community structures in comparison with CF (e.g., markedly increased the populations of Methanobacteriales and Methylomonas and suppressed Methanomicrobiales and Methylobacter populations). Methane emissions were significantly and positively related to the mcrA and pmoA gene copy numbers, as well as the mcrA/pmoA ratio. The partial least squares path model (PLS‐PM) indicated that the rice plant biomass (path coefficient = 0.64), the abundance of methanogens (path coefficient = 0.57) and the community structure of methanotrophs (path coefficient = −0.59) were determinants of CH4 emissions. Among the three residue‐treated soils, FMR showed the lowest CH4 emissions and was associated with a slight decrease in the mcrA/pmoA ratio and a significant increase in the Type I/Type II methanotrophs ratio. Thus, we recommend the co‐incorporation of Chinese milk vetch and rice straw as a sustainable fertilization pattern to improve the growth of rice and minimize CH4 emissions. Highlights: Residue application improves rice productivity (except for FR), soil fertility and CH4 emissions.Co‐incorporation of MV and RS reduces CH4 emissions in comparison with pure MV or RS addition.Residue application changes the community structure of methanogens and methanotrophs.The methanogenic abundance and the methanotrophic community structure determine the CH4 emissions. [ABSTRACT FROM AUTHOR]

In southern China, winter green manure is widely used in rice cropping systems for improving grain yields and soil fertility. Cd pollution has recently been reported in some of these paddy fields. Research on the in-depth understanding of how green manuring affects Cd absorption in rice is limited. This study aimed to investigate the impacts of different green manures, including single plantation and mixed plantation on the absorption of Cd by rice and explore the underlying mechanisms. Pot experiments demonstrated that compared with winter fallow–rice, green manuring treatments considerably decreased rice Cd content, promoted the conversion of bioavailable Cd fraction into a more stable form, induced the formation of iron plaque, and increased the content of humic-like fraction (HF) in soil dissolved organic matter (DOM). Treatment with mixed plantation resulted in a greater decrease in rice Cd content and an increase in HF and iron plaque contents than single plantation. Hydroponic experiments confirmed that both iron plaque and green manure-derived DOM significantly reduced the Cd content in rice seedlings. In conclusion, green manure incorporation is an efficient measure for the safe utilization of Cd-contaminated soil, and mixed plantation of different green manures exerts stronger effects. [Display omitted] • Green manuring significantly reduced Cd contents in rice tissues. • Green manuring enhanced humic-like fraction but reduced protein-like fraction. • Humic-like fraction and iron plaque were effective in immobilizing Cd. • DOM and iron plaque affected Cd mobility and bioaccumulation. • Mixed plantation of green manure is more effective in reducing Cd absorption. [ABSTRACT FROM AUTHOR]

Milk vetch (Astragalus sinicus L.; MV) is the most common winter green manure used in rice cropping systems in southern China. The utilization of MV can achieve the dual goals of soil fertilization and increased rice yield. Two long-term field experiments were conducted in Yujiang and Gaoan in Jiangxi Province, a typical double-rice cropping area, to explore the effects of 80 % conventional fertilizer for early rice supplemented with 15.0 (G1F80), 22.5 (G2F80), 30.0 (G3F80), and 37.5 (G4F80) t ha−1 MV on rice yield, soil fertility, nutrient uptake, and nutrient use efficiency. The results showed that, the yield data obtained from the 5-year (Gaoan) and 12-year (Yujiang) long-term experiments demonstrated that compared with conventional fertilization (F100), treatments with MV markedly increased the yield of early and late rice by 2.5–8.8 % and 5.6–10.9 %, respectively, and high rates of MV (G3F80 and G4F80) performed better in grain yields. The nitrogen (N) and potassium (K) uptake of early rice in Gaoan increased by 38.1 and 34.8 kg ha−1, respectively, and the N uptake of late rice in Gaoan and Yujiang increased by 11.7 and 62.6 kg ha−1 in G2F80, respectively, compared to that in F100. Compared with F100, treatments with MV significantly increased phosphorus (P) fertilizer recovery efficiency by 23.1–36.4 %, and the agronomic efficiency of N, P, and K fertilizers increased by 16.1–21.1 %, 13.9–19.6 %, and 15.7–21.4 %, respectively. Partial least squares path model analysis indicated that soil available P was the most important factor affecting the nutrient uptake of rice, and available K was the most important factor affecting fertilizer use efficiency. Our results suggested that 22.5 t ha−1 MV supplemented with 80 % chemical fertilizer is recommended for double-rice cropping sites to improve rice yield and crop uptake and the use efficiency of N, P, and K fertilizers. • Green manure with 80 % of N, P, and K fertilizer increased or maintained the multi-year yield. • Green manure with 80 % of N, P, and K fertilizer enhanced the grain N, P, and K uptake. • Green manuring increased the use efficiencies of N, P, and K fertilizer. • Application of 22.5 t ha−1 milk vetch with 80 % of chemical fertilizer can be recommended for double-rice cropping sites. [ABSTRACT FROM AUTHOR]

Green manuring is a potential method for reducing chemical N fertilizer input and reactive N losses to the environment that can achieve dual goals of food security and green development of agriculture. In this study, three long-term field experiments in south China and process-based model (WHCNS_LIXIM model) were combined to examine effects of long-term green manure substitution on soil N supply, crop N uptake, and N losses in rice production system. Results showed that green manure substitution significantly improves soil mineral N by 27.4–94.9% and 1.0–45.0% at jointing and maturity stages, respectively, compared with the use of chemical N alone. Moreover, 18.4–62.2% of crop N uptake increased at the maturity stage at Xinyang and Yujiang sites. The model demonstrated satisfactory performance in modeling dynamics of soil mineral N, crop N uptake, crop dry matter, and grain yield of the rice–green manure system with a determination coefficient (R2) > 0.967 and slope of linear regression equation (β) close to 1.0. Simulated N budgets presented that green manure reduces 20–40% of the chemical N fertilizer input and decreased 5.5%, 25.1%, and 30.6% of N losses by ammonia volatilization, leaching, and runoff, respectively, when green manure application rates (fresh matter) are less than 30 t ha−1. However, the total N loss increased with the increase of green manure application amounts when application amounts are larger than 30 t ha−1. These findings indicated that the further reduction of chemical N fertilizer was needed when the application amount of milk vetch was higher than 30 t ha−1. A milk vetch application of 15–30 t ha−1 was recommended to substitute 20–40% of chemical N fertilizer to improve crop N uptake and reduce N losses, and develop green rice production system in the study areas. • Long-term green manure substitution significantly improves soil mineral N. • Long-term green manure substitution enhances crop N uptake and reduces N losses. • The WHCNS_LIXIM model performed well in simulating soil mineral N and crop N uptake. • Milk vetch application of 15–30 t ha−1 was recommended to improve crop N uptake and reduce N losses. [ABSTRACT FROM AUTHOR]